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attached to a condenser. The acids are poured in through
a funnel, and a few small bits of broken unglazed pot are
dropped in to prevent bumping. The acid is distilled with a
moderate flame until about 70 c.c. have collected in the
receiver, when the operation is stopped. The distillate is then
tested for halogens by diluting largely with distilled water, and
adding silver nitrate solution. The liquid should remain per-
fectly clean It should also be tested for the presence of sul-
phuric acid, in case it is required for sulphur estimations, by


FIG. 20.

adding a few drops of barium chloride to a fresh portion of acid
diluted as above. If pure, it is kept in a stoppered bottle. If it
contains chlorine, it must be redistilled over a few crystals of
silver nitrate. Fuming nitric acid has a sp. gr. of about 1*5 at
15, boils at about 90, and contains about 90 per cent, of
HNO3. Acid of this strength can be purchased.
4. A Tube F-urnacc.  Various forms of furnace are used.
Those which are heated on the principle of the Lothar Meyer
hot-air furnace by a number of pin-hole gas jets are easily
regulated, and can be raised to a high temperature. The
Gattermann furnace, shown in the diagram (Fig. 20), is a very
convenient form.